Taxicab advertising sign



FIG. 1 is a front and top perspective view of an ornamental design for a "taxicab advertising sign" showing our new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a bottom plan view thereof;

FIG. 4 is a front end elevational view thereof; and

FIG. 5 is a side elevational view thereof.

The broken line disclosure in FIG. 1 is for illustrative purposes only and forms no part of the claimed design. 

The ornamental design for a taxicab advertising sign, substantially as shown and described. 